The present invention relates to a line illuminating apparatus for illuminating a linear region, particularly, to a line illuminating apparatus adapted for automatically inspecting a fine object to be inspected by utilizing an image processing technology.
In recent years, an inspection utilizing an image processing technology is widely employed. Particularly, in the case of inspecting a circuit pattern formed on a semiconductor chip, a liquid crystal glass substrate, a printed circuit wiring board, a lead frame for mounting a semiconductor chip or a TAB (Tape Automated Bonding) tape, it is difficult to perform the visual inspection via, for example, a microscope because the pattern has become finer and finer and the mounting density has become higher and higher. Therefore, the target object to be inspected is subjected to an image processing in general to automatically inspect whether or not the line width has a predetermined value.
In a known inspecting apparatus utilizing an image processing technology, a work to be inspected such as a glass substrate, a printed wiring board, or a TAB tape is moved in one direction at a predetermined speed. At the same time, an image of the target object to be inspected such as a circuit pattern is taken in by utilizing a line sensor consisting of, for example, a solid-state pickup device arranged in a direction perpendicular to the moving direction of the work to inspect, for example, the line width by detecting the difference in reflectivity between the substrate such as a base plate or a tape and the pattern. In such a case, an illuminating apparatus for irradiating the work with light is used in order to obtain a clear difference in concentration (difference in brightness) between the substrate and the pattern.
The conventional illuminating apparatus for illuminating a linear inspecting region includes, for example, a linear arrangement of a large number of light-emitting diodes used as a light source, a linear tube-like fluorescent lamp, an apparatus in which the light radiated from a light source is converted into a parallel light by a collimator and the parallel light is, then, converted into a linear light by a cylindrical lens, and another apparatus in which the light radiated from a light source of hundreds of watts is guided by a large number of optical fibers to a region near an illuminating line L, the distal ends of the optical fibers being arranged to form a linear light.
However, the conventional illuminating apparatus having a linear light ray is constructed to illuminate the target object in one direction. Therefore, when viewed from the side of the target object to be illuminated, the brightness differs depending on the viewing direction. For example, where the work has an irregular surface or an opening, bright and dark portions appear in the irregular surface portion. Also, the light is strongly reflected from the edge of the opening to form a bright portion. As a result, it is impossible to perform the inspection, or an erroneous judgment is brought about. Such being the situation, it is necessary to use a dome-shaped illuminating apparatus in which the entire linear illuminating region is covered with a hemispherical member and the entire inner surface of the hemispherical member is allowed to emit light with a uniform brightness. Since the brightness of the dome-shaped illuminating apparatus is isotropic as viewed from the target object, bright and dark portions are not generated, and it is possible to prevent an erroneous inspection result from being derived from the presence of the irregular surface portion.
However, since the dome-shaped illuminating apparatus outlined above uniformly illuminates a very large space, though it suffices to illuminate a small linear region, the loss of energy required for the illumination is very large. In addition, it is difficult to obtain a brightness sufficient for the inspection.
An object of the present invention, which is intended to overcome the above-noted defects inherent in the prior art, is to provide a line illuminating apparatus that permits suppressing the loss of the energy required for the illumination and also permits preventing the inspection from being affected by the presence of irregularity on the surface of a target object to be inspected.
According to the present invention, there is provided a line illuminating apparatus, comprising a light source and a light guide for guiding the light emitted from the light source to a predetermined irradiating line, wherein the light-emitting surface at the distal end of said light guide is in the form of a semicylinder covering the irradiating line.
It is desirable to divide the semicylindrical plane in the circumferential direction into a plurality of sections each consisting of the light emitting surface of a plate-like light guide. It is also desirable to coarsen the light emitting surface of the light guide to permit the emitted light to be diffused in the axial direction of the semicylindrical plane.
In the line illuminating apparatus of the present invention constructed as described above, the light emitting surfaces of the light guides are arranged to define a imaginary semicylindrical plane extending along the irradiating line. The particular construction makes it possible to make the distance between the irradiating plane to be irradiated and the light emitting planes of the light guides markedly shorter than that in the dome-shaped illuminating apparatus. As a result, the region to be illuminated is diminished to markedly eliminate the energy loss required for the illumination while ensuring the brightness required for the inspection easily and without fail. In addition, since the light emitting surfaces are arranged to define a imaginary semicylindrical plane in a manner to cover the irradiating line, the brightness as viewed from the irradiated plane is rendered isotropic. It follows that, even if an irregularity such as a stepped portion or an opening is present on the work such as a semiconductor substrate, a glass substrate for a liquid crystal display device, a printed wiring board, a lead frame or a TAB tape, it is possible to prevent bright-dark portions from being generated in the irregular portion and to prevent an edge portion of the opening from being strongly reflected, making it possible to eliminate the incapability of inspection and an erroneous inspection.
The light emitted from the light guide has directivity in general, with the result that the intensity of the emitted light tends to be weaker in the peripheral portion than in the central portion of the light emitting surface. For overcoming this difficulty, the semicylindrical plane is divided in the present invention in the circumferential direction into a plurality of sections each consisting of the light emitting surface of the plate-like light guide, making it possible to further improve the isotropy of brightness. Further, since the light emitting surfaces are arranged to define a semicylindrical configuration, the both end portions in the axial direction are rendered dark when viewed from the irradiated surface. To overcome this difficulty, the light emitting surface is coarsened to have anisotropy such that the light emitted from the light emitting surface is diffused in the axial direction of the semicylinder, thereby correcting the darkness in the axial direction of the semicylinder. It follows that it is possible to diminish the influences given by the irregularity or opening present on the work.